THE MITOCHONDRIAL OUTER-MEMBRANE PROTEIN MAS22P IS ESSENTIAL FOR PROTEIN IMPORT AND VIABILITY OF YEAST

We have cloned the gene encoding the protein Mas22p, which spans the o uter membrane of yeast mitochondria. Cells that completely lack Mas22p are inviable. The plasmid-borne MAS22 gene suppresses several defects resulting from the deletion of one or more of the mitochondrial prote in import receptors. Defects of Mas20p-deficient cells are explained b y the reduced level of Mas22p in these mutants. Mas22p has one acidic domain in the cytosol and a second acidic domain in the mitochondrial intermembrane space. We suggest that these domains of Mas22p on either side of the outer membrane function as a relay system for transferrin g the basic targeting sequences of precursor proteins into the mitocho ndria.